Joe, there are two oil pressure sending units on the Cummins ISX. One is installed by Cummins and feeds the engine ECM (electronic control module). The other is installed by Monaco and feeds the dash gauge and warning light.
Does your dash oil pressure gauge work? This is fed from the VDO 2 post sending unit just above the starter.
Link to new VDO sending unit:
Does your Aladdin read the correct oil pressure? This is a 3 prong unit fed from the ECM. Usually if this reads incorrect it will shut down the engine.